7.6-15. Show that a $100(1-\gamma) \%$ confidence interval for $\sigma^{2}$ is $$ \left(\frac{\sqrt{\sigma} \overline{\sigma^{2}}}{\chi_{\gamma / 2}^{2}(n-2)}, \frac{n \widehat{\sigma^{2}}}{\chi_{1-\gamma / 2}^{2} (n-2)} ight) $$ SP.PB. 174